Maryland Grows

Gardeners are made of tough stuff. We manage a brave smile when our seedlings get nibbled, our leaves go spotty and the blessed groundhogs help themselves to our harvest.  

But there is one affliction that bring tears to our eyes: squash vine borers. I just felt the shudders from those of you who’ve had a close encounter. It’s awful.  

Picture if you will a robust squash plant, deep green, full of flowers and fruit, tall enough to shade several small children. The next morning as you sip your coffee, you spy it out your kitchen window, wilted, flattened, gone.

Yes, your neighbors heard you wail.  

What happened? Squash vine borers. These insidious insects tunnel inside squash as larvae, happily munching away as they fatten. Finally they hollow out enough of the plant that it collapses, its vascular system vanquished.

Squash vine borers most often hit summer and winter squash and pumpkins. But they can go after cucumbers, gourds and melons, too.  

So how do you prevent this tragedy? There are several good preventive measures and treatments.  

One trick is to plant early. Every insect has a prime time and simply planting earlier helps you avoid squash vine borers’ window of activity. It pays to know the enemy. 

Use established transplants instead of seeds or plant squash seeds mid-June. Again, it’s all about timing.  

You can prevent flying adults from laying eggs on your plants in May and June one of three ways. Wrap a collar of aluminum foil around the lower stems. Dust or spray with spinosad or pyrethrum. Or, cover your plants with floating row covers until they flower.  

Check your squash plants daily for signs of larval feeding. If a runner suddenly wilts, there’s probably a borer in there doing its worst.  

Also look at the base of your plants for holes and tan, sawdust-like bits. As borer larva feed, they push out frass, a fancy word for insect poop. If you find any, the game’s afoot.

Use a knife to make a slit upward from where you see frass. Cut halfway through the stem and remove and kill the larva, a white caterpillar with a dark head. Mound soil over the cut to promote healing. 

If you’re squeamish about squishing, inject Bt – a naturally occurring soil bacteria and organic insecticide – into the wound to kill the borer.  

If you remove an infested vine, seal it in a plastic bag and put it in the trash. This prevents the larva from dropping to the ground to pupate and return to infest your plants next year. 

I just heard Arnold say, “I’ll be back.”  

It also helps to know which squash the vine borers prefer. Butternut and cushaw squash are resistant to borers. Yellow crookneck squash is less likely to get borers than zucchini.  

Don’t give up on squash. I for one will not be without butternut squash soup. And Halloween without pumpkins is unthinkable. So prepare, prevent, and treat wisely to keep enjoying squash.

By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. This article was previously published by Herald-Mail Media. Read more by Annette.